1. Industrial Useful Field
This invention relates to a stepless speed-change power transmission for vehicle having a fluid coupling, a forward/backward change-over mechanism coupled to a rear stage of the fluid coupling and a stepless speed changer coupled to a rear stage of the forward/backward change-over mechanism.
2. Prior Art and Its Problem
Dry centrifugal clutches or a hydraulic clutch have have heretofore been proposed for stepless speed-change power transmissions. More recently in, (Unexamined Japanese patent publication No. 57-140956) a fluid coupling equipped with a lock-up device or a torque converter is proposed, which provides smooth acceleration and improved fuel consumption.
However, such fluid coupling or torque converter has a problem that, when the vehicle is stopped and the engine continues running, the engine power is transmitted to the speed changer side and can cause an unexpected sudden acceleration of the vehicle, for example, when the engine rotation rises sharply during warm-up. This phenomenon is commonly referred to as creep.
To overcome such creep, an automatic transmission incorporating a clutch in the speed changer at the rear stage of the fluid coupling has been proposed. However, a transmission equipping a mechanism for preventing such creep phenomenon in the fluid coupling has not been developed yet.